Function Generator




Circuit Schematic

The function generator uses an XR2206 IC sine-triangle-square wave IC. Frequency is set by switch S1 and variable resistor VR1.
Amplitude is set by preset pots P1 and P2. Sine wave distortion is adjusted by P3 and symmetry by P4. The XR 2206 open collector
square wave output is bootstrap buffered to assure equally fast rising and falling edges. Switch S2 selects sine, triangle or
square wave and applies it to output buffer opamp U2. S2 also mutes the square wave when not used and selects the correct
amplitude on sine or triangle waves. The output from the buffer amplifer is fed to output socket and the square wave is
attenuated and fed to the sync output socket.



Circuit Board

The circuit is built on a Vero stripboard, and is laid out so that connectors are close to controls and preset pots
are accessible when the instrument is assembled with the battery box over the circuit board.



Board Installed in Case





Front Panel

The controls are:
top row centre: sine-triangle-square switch
bottom row: freq range switch, freq coarse, freq fine, amplitude




Rear Panel




Function Generator with Frequency Meter - front view



Function Generator with Frequency Meter - rear view

This is how the two instruments will normally be used. The counter output of the function generator aligns with the
counter input and is connected via BNC-to-terminal adaptors. Supplies are separately switched because the meter is
more power hungry than the function generator and can be switched off to save battery when not needed.

It should be stressed that this is not a professional quality function generator. The board used is an experimenters'
kit which is supplied with on-board mini switches. It has been developed here to create a low cost compact source of
sine and square waves for experimental use.

It is battery powered and has a very small footprint, only 5" wide by 4" deep.

Professional instruments use split power supplies and are direct coupled with dc offset, am modulation and fm
modulation capability. They are much larger, heavier and mains powered.


Frequency Bands
Tuning bands are approximately:
Low Band: 10Hz - 50Hz - 500Hz
Med Band: 400Hz - 2kHz - 20kHz
High Band: 10kHz - 50kHz - 500kHz
The middle figures are the frequencies with the reverse log tuning pot set half way.

Output Amplitude
Square wave amplitude is a little over 2V peak to peak.
Sine and triangle wave outputs are set to 2V peak-to-peak.



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